Box projection for reflection probes

Original issue: https://github.com/microsoft/MixedRealityToolkit-Unity/issues/9150

Describe the problem

Box projection doesn't seem to work on the MRTK standard shaders, which causes really bad reflective surfaces for head mounted displays (especially in rooms)

Describe the solution you'd like

Enable box projection for reflection probes to work with the MRTK standard shader

Describe alternatives you've considered

Writing some custom shader

Additional context

the MRTK/Standard shader does not account for box projection (or reflection probe blending). We should call this out in the docs.

To properly support box projection we need to introduce a call to the BoxProjectedCubemapDirection method within UnityStandardUtils. There is a great example of the changes need on this page: https://catlikecoding.com/unity/tutorials/rendering/part-8/

Thanks @Cameron-Micka I tweaked the shader so the worldReflection parameter reads as follows:

float3 worldReflection = BoxProjectedCubemapDirection(reflect(incident, worldNormal), i.worldPosition, unity_SpecCube0_ProbePosition, unity_SpecCube0_BoxMin, unity_SpecCube0_BoxMax);

I didn't add blending as I didn't need it (yet), so this does the trick so far

Beginne damit, den MRTK standard shader und seine Verwendung von UnityStandardUtils zu lokalisieren, und vergleiche anschließend den Pfad für Reflection Probes mit dem im Issue verlinkten Beispiel BoxProjectedCubemapDirection. Als abgeschlossen gilt die Aufgabe, wenn die Box-Projektion für Reflection Probes im MRTK standard shader funktioniert und das relevante Shader-Verhalten auf reflektierenden Oberflächen verifiziert wurde.